I've seen trailers use 235/85R16s before. I think 7000 lb axles are usually 8 on 6.5.

I've always had the feeling that the majority of trailer tire failures that happen are due to poor maintenence and people banging their trailers into things like curbs, fences, etc. That, and people using cheap-o tires on their trailers, $40 specials or old car tires.

I haven't ever had a tire failure, per se. I once had a tire tire lose some tread (didn't lose air, but was thumping badly) on a construction trailer (back when I worked landscape for 3 years and pulled a trailer daily). Those trailers say daily use and the tires were old. I also damaged a sidewall once pulling out of my back yard (had bought a new trailer, didn't realize it was wider than the old one, and I clipped my chain link fence). I parked the rig in the driveway and replaced it with a new once, before continuing, though.

You just don't see people blowing tires on their tow rigs all the time, so why do people have problems on their trailers? low air pressure, scuffed sidwalls, improper loading? Are truck tires tougher, or to trailer tires see more damage?

I't d be kinda cool to design the trailer to have the same bolt pattern and tire size as your tow vehicle (if possible), so you'd have spare tires that could work for either vehicle.